Factors influencing bone formation and resorption will be examined in organ culture and in vitro using quantitative morphology, biochemical analysis of collagen and non-collagen protein synthesis, and calcium uptake and release. Factors to be studied include parathyroid hormone, active metabolites of vitamin D, insulin, glucocorticoids, prostaglandins, osteoclast activating factor, and stimulator of bone resorption and formation found in serum.